P0852

Park/Neutral Switch Input Circuit High

Indicator

The PCM has detected a malfunction in the park/neutral switch input circuit. The transfer case shift selector range sensor inputs data to the PCM where it is utilized to calculate engine RPM, fuel delivery strategy, and engine timing, among other things. This code applies to vehicles equipped with four-wheel drive and an automatic transmission only.

Code Set Parameters

If the PCM receives inputs from the vehicle speed sensor, transmission shift solenoids, torque converter lock-up solenoid, or other sensors, indicating that the vehicle is being operated in an incorrect transmission shifter range a code will be stored and a malfunction indicator lamp may be illuminated. The transmission may also be placed in limp-in mode by the PCM.

Symptoms

Common Causes

By far the most common cause of this code is from a misadjusted transfer case range sensor. Other causes may include a defective range sensor, open, shorted, corroded, or otherwise damaged wiring and/or electrical connectors. If recent transmission repairs have been performed, suspect that the range sensor was not readjusted properly. Sensor retaining bolts should always be installed using thread locking compound to ensure proper torque longevity. Technicians also report the presence of excessive corrosion in the sensor connector as the cause of this code being stored.

Common Misdiagnosis

The transfer case range sensor is frequently replaced in error when a simple adjustment will correct the complaint.

Diagnosis

A scanner (or code reader) and a digital volt/ohmmeter will be helpful in successfully diagnosing this code-storing condition.
The park/neutral switch is used to determine (for the PCM) which gear the transfer case is placed in

Most park/neutral switches are of a variable resistance variety

The switch is positioned over the transfer case shift shaft and the shift lever slides on over it

As the shift lever is moved (via the shift lever in the cockpit and the shifter cable) the range sensor pivot is moved to different contacts

The PCM reads the varying levels of voltage, regulated by the differing levels of resistance in the switch contacts, as the gears in which the transfer case shifter are placed

As transmission, ABS, and engine inputs are received by the PCM, it determines whether or not the transfer case is in the correct gear for the driving conditions and reacts accordingly.
Begin your diagnosis with a visual inspection of system wiring, connectors, and components

Repair or replace any open, shorted, damaged, or corroded items as required and retest the system to make sure that repairs were successful.
If the system wiring, connectors, and components appear to be in normal working order, connect the scanner to the diagnostic connector and record all stored trouble codes and freeze frame data

This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored

After the codes are cleared, operate the vehicle to see if the code returns

If the code fails to immediately return, you may have an intermittent condition

Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made

If the code immediately returns, check for battery voltage and ground signals at the park/neutral switch

If either the ground or battery voltage circuits are open, use the digital volt/ohmmeter to check for continuity (disconnect all related control modules from the circuit before checking circuit resistance or controller damage may occur) and resistance in both circuits

Repair or replace system circuits/connectors as required and retest the system to ensure that repairs were successful.
Carefully disconnect electrical connectors to all related controllers

Using the manufacturer’s wiring diagram for the park/neutral switch, test all related circuits and the sensor for resistance and continuity and compare your findings with manufacturer’s specifications

Repair or replace system circuitry, connectors, and/or components that fail to coincide with manufacturer’s specs

Always retest the system to ensure a successful repair.
If all circuits coincide with manufacturer’s specifications, suspect a defective PCM

Remember that PCM failure is rare and replacement will require reprogramming